(1) Field of the Invention
The present invention relates to a solid-state imaging device that converts an incident light into an electrical signal and outputs the electrical signal as a video signal.
(2) Description of the Related Arts
Solid state imaging devices are conventionally known that convert an incident light into an electrical signal and output the electrical signal as a video signal, as well as digital still cameras (DSC) that display an image based on the video signal obtained from the solid-state imaging device. In recent years such cameras incorporated with the solid-state imaging device have shown significant progress in image quality and functions, including micronization of a pixel driven by increase in number of pixels.
Regarding the solid-state imaging device, driving methods that decrease the number of pixels in the outputted video signal have been proposed, for improving an output speed of the video signal. The proposed methods include, for example, decimating the pixels to be read out in directions of column and row at a predetermined pitch, and mixing signal charges of a plurality of pixels. As a method for decimating or mixing the pixels, a distribution transfer unit provided between a vertical transfer unit and a horizontal transfer unit for controlling transfer of a signal charge has been proposed, for example as disclosed in PTL 1 (Japanese Unexamined Patent Application Publication No. 2006-13176).
The distribution transfer unit includes independent transfer electrodes provided for each column for independent control, to thereby control the transfer of a signal charge from the vertical transfer unit to the horizontal transfer unit.
Referring to FIGS. 6A, 6B, and 7, an interconnect for electrical connection to the distribution transfer electrode for controlling a signal charge with the distribution transfer unit will be described, on the basis of a conventional solid-state imaging device.
FIG. 6A is a plan view showing a configuration of a solid-state imaging device that includes a conventional charge coupled device (CCD).
A pixel region 1300 includes a photoelectric conversion unit 1100 that converts an incident light into a signal charge, and a vertical transfer unit that transfers the signal charge in a vertical direction (downward in FIG. 6A). The vertically transferred signal charge undergoes a control by the distribution transfer unit while being transferred to a horizontal transfer unit 1120. The signal charge transferred to the horizontal transfer unit 1120 is transferred in a horizontal direction (to the left in FIG. 6A), to be read out by an output unit that converts the signal charge into a voltage and outputs the voltage.
FIG. 6B is a schematic diagram of the distribution transfer unit including independent drive electrodes aligned in the column direction that control the reading of the signal charge from the pixel region 1300 into the horizontal transfer unit 1120, in the conventional solid-state imaging device. As shown therein, the vertical transfer unit of the distribution transfer unit has the same electrode structure by every 2n+1 (n is an integer not smaller than 1) columns, and includes independent drive electrodes separated from each other in an island shape.
The transfer of the signal charge by the distribution transfer unit is controlled by a voltage applied to the distribution transfer electrode through a shunt interconnect connected thereto. As shown in FIG. 6A, a part of the shunt interconnect makes electrical connection between a bus line interconnect provided at a position beyond the horizontal transfer unit 1120 (lower portion in FIG. 6A) and the distribution transfer electrodes of the distribution transfer unit.
FIG. 7 is a plan view showing a detailed interconnect layout in the distribution transfer unit.
As shown in FIG. 7, the interconnect on the distribution transfer unit includes, unlike in the pixel region, a first interconnect 1170 (tungsten according to PTL 1) and a second interconnect 1180 (aluminum according to PTL 1). The first interconnect 1170 and the second interconnect 1180 are electrically connected through a contact at a predetermined position 1410.
Another example of power supply to the distribution transfer electrode, which serves to perform the decimation as above, can be found in PTL 2 (Japanese Unexamined Patent Application Publication No. 2008-193050) which proposes extending an interconnect over the horizontal transfer unit from the shunt interconnect provided thereon, and also extending an interconnect from the shunt interconnect on the pixel region in a vertical transfer direction.
FIG. 8 is a plan view showing a configuration of the portion around the distribution transfer unit of the conventional solid-state imaging device.
The distribution transfer unit includes a hold gate portion 117, a storage gate portion 121, and a charge storage unit VOG. Shunt interconnects 171 to 176 make electrical connection to each electrode (polysilicon of second layer in PTL 2) through contacts of interconnects 181 to 183 horizontally provided on the pixel region and interconnects 184 to 186 provided on the horizontal transfer unit.